When antennas are installed in proximity to one another on aircraft or other objects, there can be interaction between the fields of the antennas resulting in unwanted coupling between the antennas. Attempts have been made to reduce the side lobe energy emitted from the antennas, particularly horn antennas, in order to attenuate this unwanted coupling between the antennas. Corrugated surfaces on the internal walls of a horn antenna have been used in an attempt to accomplish this. The theory of the corrugated surface is that each depression in the corrugation acts as a short-circuited waveguide one quarter wavelength deep to a surface wave traveling across it, so that the reflected energy from it is in opposite phase to the incident energy and will tend to cancel it out, thereby reducing the side lobes energy. However, such corrugated surfaces are difficult and expensive to fabricate. Another means utilized to reduce the side lobe energy consists of placing an absorbing hood forward of the aperture of the antenna horn in order to absorb energy from the side lobes, but such structure consumes space and may interfere with the use of the antenna.